10.1002/anie.202002900
Angewandte Chemie International Edition
RESEARCH ARTICLE
[2]
[3]
a) F. Minisci, R. Bernardi, F. Bertini, R. Galli, M. Perchinummo,
Tetrahedron 1971, 27, 3575-3579; b) Li J.J. (2009) Minisci reaction. In:
Name Reactions. Springer, Berlin, Heidelberg.
resultant alkyl radical to protonated lepidine, affords a radical
cation III. This transient species losses a proton to give radical IV.
In the final step, IV undergoes highly exothermic oxidation,
mediated by CeIV, to generate the final alkylated quinoline product.
On the other hand, the requisite carbamoyl radical VI for the
a) L. Candish, M. Freitag, T. Gensch, F. Glorius, Chem. Sci. 2017, 8,
3618-3622; b) R. A. Garza-Sanchez, A. Tlahuext-Aca, G. Tavakoli, F.
Glorius, ACS Catal. 2017, 4057-4061; c) Z. Li, X. Wang, S. Xia, J. Jin,
Org. Lett. 2019, 21, 4259-4265; d) A. H. Jatoi, G. G. Pawar, F. Robert,
Y. Landais, Chem. Commun. 2019, 55, 466-469; e) D. R. Sutherland, M.
Veguillas, C. L. Oates, A.-L. Lee, Org. Lett. 2018, 20, 6863-6867; f) J. D.
Galloway, D. N. Mai, R. D. Baxter, Org. Lett. 2017, 19, 5772-5775; g) M.
Jouffroy, J. Kong, Chem. Eur. J. 2019, 25, 2217-2221; h) M. T.
Westwood, C. J. C. Lamb, D. R. Sutherland, A.-L. Lee, Org. Lett. 2019,
21, 7119-7123.
carbamoylation
reaction
is
generated
through
the
thermodynamically favorable single-electron transfer (SET)
oxidation of the oxamate substrate (Ep/2ox = 1.17 V vs SCE) by the
red
photocatalyst in its excited state (Ep/2 (4CzIPN*/·−) = 1.35 V vs
SCE), followed by decarboxylation. In this case, the aromatization
of radical cation VII through tandem deprotonation and oxidation
(path a) is less likely due to the absence of chemical oxidants in
[4]
[5]
S. Caron, R. W. Dugger, S. G. Ruggeri, J. A. Ragan, D. H. Ripin, Chem.
Rev. 2006, 106, 2943-2989.
the reaction system. The lower reduction potential of 4CzIPN
red
(Ep/2red = −1.22 V vs SCE) over the protonated product X (Ep/2
=
a) S. Tang, L. Zeng, A. Lei, J. Am. Chem. Soc. 2018, 140, 13128-13135;
b) H. Wang, X. Gao, Z. Lv, T. Abdelilah, A. Lei, Chem. Rev. 2019, 119,
6769-6787.
−0.72 V vs SCE) suggests that the oxidation of radical VIII with
4CzIPN is thermodynamically unfavorable. The detection of
dihydroquinoline during the synthesis of 6 implies that VII accepts
an electron from the persistent and highly reducing catalyst-
derived radical anion V to afford intermediate IX. The high
exothermicity for the reduction of VII with V suggests that this
process is extremely fast and competes well with the
deprotonation pathway. Ultimately, the anodic oxidation of IX,
which is highly stable, leads to the final carbamoylation product X.
For both oxidative C–H functionalization reactions, protons are
reduced at the cathode to produce H2.
[6]
a) J. Koeller, P. Gandeepan, L. Ackermann, Synthesis 2019, 51, 1284-
1292; b) W.-F. Tian, C.-H. Hu, K.-H. He, X.-Y. He, Y. Li, Org. Lett. 2019,
21, 6930-6935.
[7]
[8]
[9]
B. Chen, L.-Z. Wu, C.-H. Tung, Acc. Chem. Res. 2018, 51, 2512-2523.
X. Sun, J. Chen, T. Ritter, Nat. Chem. 2018, 10, 1229-1233.
a) H. Kolbe, Ann. Chem. Pharm. 1848, 64, 339-341; b) H. J. Schäfer, in
Comprehensive Organic Synthesis (Eds.: B. M. Trost, I. Fleming),
Pergamon, Oxford, 1991, pp. 633-658; c) H. Kurihara, T. Fuchigami, T.
Tajima, J. Org. Chem. 2008, 73, 6888-6890.
[10] a) J. Xiang, M. Shang, Y. Kawamata, H. Lundberg, S. H. Reisberg, M.
Chen, P. Mykhailiuk, G. Beutner, M. R. Collins, A. Davies, M. Del Bel, G.
M. Gallego, J. E. Spangler, J. Starr, S. Yang, D. G. Blackmond, P. S.
Baran, Nature 2019, 573, 398-402; b) T. Tajima, H. Kurihara, T.
Fuchigami, J. Am. Chem. Soc. 2007, 129, 6680-6681.
Conclusion
In
summary,
we
have
achieved
oxidant-free,
[11] A. Matzeit, H. J. Schäfer, C. Amatore, Synthesis 1995, 1432-1444.
[12] Zeng reported exciting electrochemical C–H acylation of diazines, albeit
with limited scope: Q.-Q. Wang, K. Xu, Y.-Y. Jiang, Y.-G. Liu, B.-G. Sun,
C.-C. Zeng, Org. Lett. 2017, 19, 5517–5520.
electrophotochemically driven C–H alkylation and carbamoylation
of electron-deficient N-heteroaromatics with carboxylic acids and
oxamic acids, respectively, through H2 evolution. While
electrochemistry or photocatalysis alone proves inadequate, the
merger of the two technologies allows the complementation of
their respective strengths, leading to efficient decarboxylative C–
H functionalization reactions. Essential to the success is the
development of conditions to allow the generation of alkyl or
carbamoyl radicals from the corresponding carboxylic acids under
acidic conditions. The effective coupling of decarboxylative
radical formation and hydrogen evolution opens new
opportunities in developing sustainable oxidative radical reactions.
[13] Selected recent reviews: a) C. K. Prier, D. A. Rankic, D. W. C. MacMillan,
Chem. Rev. 2013, 113, 5322-5363; b) N. A. Romero, D. A. Nicewicz,
Chem. Rev. 2016, 116, 10075-10166; c) L. Marzo, S. K. Pagire, O.
Reiser, B. König, Angew. Chem. Int. Ed. 2018, 57, 10034-10072; d) J.
Xuan, W.-J. Xiao, Angew. Chem. Int. Ed. 2012, 51, 6828-6838; e) J. M.
R. Narayanam, C. R. J. Stephenson, Chem. Soc. Rev. 2011, 40, 102-
113.
[14] Selected recent reviews: a) M. Yan, Y. Kawamata, P. S. Baran, Chem.
Rev. 2017, 117, 13230–13319; b) S. R. Waldvogel, S. Lips, M. Selt, B.
Riehl, C. J. Kampf, Chem. Rev. 2018, 118, 6706–6765; c) Q.-L. Yang, P.
Fang, T.-S. Mei, Chin. J. Chem. 2018, 36, 338–352; d) R. Francke, R. D.
Little, Chem. Soc. Rev. 2014, 43, 2492–2521; e) K. D. Moeller, Chem.
Rev. 2018, 118, 4817–4833; f) J. E. Nutting, M. Rafiee, S. S. Stahl, Chem.
Rev. 2018, 118, 4834–4885; g) J. Yoshida, A. Shimizu, R. Hayashi,
Chem. Rev. 2018, 118, 4702–4730; h) M. D. Kärkäs, Chem. Soc. Rev.
2018, 47, 5786-5865; i) Y. Yuan, A. Lei, Acc. Chem. Res. 2019, 52, 3309-
3324; j) N. Sauermann, T. H. Meyer, Y. Qiu, L. Ackermann, ACS Catal.
2018, 7086–7103; k) P. Xiong, H. C. Xu, Acc. Chem. Res. 2019, 52,
3339-3350; l) Y. Jiang, K. Xu, C. Zeng, Chem. Rev. 2018, 118, 4485–
4540.
Acknowledgements
Financial support of this research from National Key R&D
Program of China (2016YFA0204100), NSFC (21672178,
21971213) and the Fundamental Research Funds for the Central
Universities.
[15] H. Yan, Z.-W. Hou, H.-C. Xu, Angew. Chem. Int. Ed. 2019, 58, 4592-
4595; Angew. Chem. 2019, 131, 4640–4643.
Keywords: electrochemistry • photocatalysis • heterocycles • C-
H functionalization • radical reactions
[16] a) L. Capaldo, L. L. Quadri, D. Ravelli, Angew. Chem. Int. Ed. 2019, 58,
17508-17510; b) J. P. Barham, B. König, Angew. Chem. Int. Ed. 2019,
10.1002/anie.201913767; c) Y. Qiu, A. Scheremetjew, L. H. Finger, L.
Ackermann, Chem. Eur. J. 2019, 10.1002/chem.201905774; d) L. Zhang,
L. Liardet, J. Luo, D. Ren, M. Gratzel, X. Hu, Nat. Catal. 2019, 2, 366-
373; e) H. Huang, Z. M. Strater, T. H. Lambert, J. Am. Chem. Soc. 2020,
10.1021/jacs.9b11472; f) H. Huang, Z. M. Strater, M. Rauch, J. Shee, T.
J. Sisto, C. Nuckolls, T. H. Lambert, Angew. Chem. Int. Ed. 2019, 58,
[1]
a) R. S. J. Proctor, R. J. Phipps, Angew. Chem. Int. Ed. 2019, 58, 13666-
13699; Angew. Chem. 2019, 131, 13802–13837; b) M. A. J. Duncton,
MedChemComm 2011, 2, 1135-1161; c) Y. Wei, P. Hu, M. Zhang, W. Su,
Chem. Rev. 2017, 117, 8864-8907.
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